1. Technical Field
The present disclosure relates to the architecture of a device having a galvanic optocoupling and, more specifically, to the galvanic optocoupling of at least one light source and an optical detector, optically connected through a transmission means and having at least one input terminal and one output terminal, the light source and the optical detector connected to respective first and second voltage references.
2. Description of the Related Art
As is known, certain applications require the use of components able to ensure a certain galvanic insulation between two different ports of a system, without penalizing the passage of a signal that encodes or contains a piece of information in the system itself. To this purpose, the use of galvanic optocouplers is known, i.e., devices able to transfer the desired information by means of an optical signal with suitable insulation characteristics.
This solution, widely present on sale, is usually realized by suitably assembling a light source, such as for example a light emitting diode (LED), realized with direct-gap semiconductors (type III-V) and a detector, such as for example usually a photodiode or a phototransistor, typically realized by silicon.
In substance, a galvanic optocoupler is essentially a safety device that allows two different sections, in particular an input stage and an output stage, of a system to exchange commands and information in a unidirectional way while remaining separate from the electric point of view. In particular, the signal transmission through the galvanic optocoupler occurs by means of light pulses that pass through an insulation layer transparent to light but with high dielectric rigidity.
An optical coupling thus occurs between the two parts of the system connected by the galvanic optocoupler which, however, remain electrically insulated one from the other (in particular, they do not have ground terminals in common).
A galvanic optocoupler of the known type is schematically shown in FIG. 1, globally indicated with 1. In particular, the galvanic optocoupler 1 connects a first circuit node, or input IN, to a second circuit node, or output OUT, ensuring the galvanic insulation of the respective voltage references GND1 and GND2 due to the conversion of an input electric signal into an optical signal.
The galvanic optocoupler 1 thus includes an input stage, in particular a light or optical source 2 connected, through an intermediate stage 3 realized by a transmission means, and in particular an insulation layer, to an output stage or optical detector 4. In particular, the insulation layer of the intermediate stage 3 is a means suitable for transmitting an optical signal (indicated with Light in the figure).
More in particular, the input or transmitter optical source 2 or transmitter emits a power that is transferred to the optical detector 4 or output photodetector. In this way, if the transmission means 3 through which the transmitter and photodetector communicate shows a good transparency and a good degree of electric insulation, the galvanic optocoupler 1 completely realizes the transmission functionality and simultaneous insulation requested.
For realizing a galvanic optocoupler device an assembly technique must be used that provides a good optical coupling between source and detector, without penalizing the galvanic insulation between the input and output gates of the device itself.
Two assembly techniques are known and widely used in the optoelectronic field that obtain a galvanic optocoupler device having these characteristics, and in particular:
1) face to face assembly technique.
This technique, schematically shown in FIG. 2A, consists in facing an optical source 2 and an optical detector 4, by means of respective self-aligned frames 2a and 3a electrically separated between input and output. The optical coupling is ensured in that the optical detector 4 is directly lightened by the optical source 2, while the galvanic insulation is obtained using an insulating, optically transparent resin inserted between the two components according to the transmission means 3.
2) dielectric mirror assembly technique.
This technique, schematically shown in FIG. 2B, consists in the use of an optical reflector 5 (or dome) which concentrates and conveys part of the optical power emitted by the optical source 2 onto the optical detector 4, both glued on a planar frame 6 with two islands that electrically separate the input from the output. An insulating, optically transparent resin incorporates the optical source 2 and the optical detector 4 and serves as support for the realization of the optical reflector 5 with function of transmission means 3. Finally, the galvanic optocoupler device includes a containment package 7.
The use of an insulator with magnetic transmission or i-coupler, as galvanic optocoupler device, as schematically shown in FIG. 2C is also known.
In particular, the i-coupler structure there shown has been obtained in the so called “Coreless Transformer” technology, as described for example in the article by Munzer et al. entitled “Coreless transformer a new technology for half bridge driver IC's”, PCIM 2003 Conference, Nuremberg, 2003.
In this structure, a primary coil 2a and a secondary coil 4a comprise respective integrated circuits, 2b and 4b, provided with respective active parts, 2c and 4c. In particular, the active part 2c of the primary coil 2a is realized above an insulation layer 3a and magnetically communicates with the secondary coil 4a through its corresponding active part 4c. 
In particular, in the structure shown in FIG. 2C, the primary coil 2a is connected to its active part 2c by means of suitable conductive paths 8 while the secondary coil 4a is connected to its active part 4c by means of suitable bonding wires 9.
Although advantageous under several aspects, these solutions are not however exempt from drawbacks. In particular, in the face to face assembly technique, the realization of two different support frames of optical source 2 and optical detector 4 as well as their alignment is problematic, in particular expensive. The step of gluing the respective elements to these support frames is as much difficult.
Similarly, the dielectric mirror assembly technique requires the use of at least two different molding compounds; in particular the compound realizing the optical reflector 5 is very expensive and difficult to be dispensed.
Finally, further difficulties can be found in the realization of the magnetically connected active parts of the primary and secondary coil in the case of the “Coreless Transformer” assembly technique.
One technical problem addressed by the present disclosure is that of devising an architecture of a device having galvanic optoinsulation suitable for being completely integrated by using integration process flows widely employed in the field of microelectronics, overcoming the limits and drawbacks still affecting the galvanic optocoupler devices realized according to prior designs and the related assembly techniques.